1. Field of the Invention
The present invention relates to a control device of an internal combustion engine having multiple injectors on an intake side of each of cylinders of the internal combustion engine respectively.
2. Description of Related Art
Patent document 1 (JP-A-S63-94057) describes a system that provides two injectors on an intake side of each cylinder of an internal combustion engine and that injects fuel into each cylinder by the two injectors, aiming at atomization of a fuel spray inside each cylinder of the internal combustion engine, reduction of port wetting (i.e., reduction of fuel adhesion to an intake port inner wall surface), and the like.
The inventors of the present invention are studying an abnormality diagnosis technology for specifying a cylinder causing an abnormal air-fuel ratio due to an abnormality in an injector in an internal combustion engine providing two injectors on an intake side of each cylinder respectively when either one of the two injectors of each cylinder becomes abnormal and for specifying which one of the two injectors of the abnormal cylinder is abnormal. During the process of the study, existence of following problems was newly found.
When either one of the two injectors of a certain cylinder becomes abnormal, the abnormal injector is specified and failsafe control is performed to prohibit an injection operation of the abnormal injector and to perform increase correction of injection quantity of the normal injector such that the fuel quantity equivalent to request injection quantity is injected only by the normal injector. In this case, it is necessary to inject the injection quantity of the two injectors (i.e., the request injection quantity) with the single normal injector. Therefore, there is a possibility that the injection quantity of the two injectors (i.e., the request injection quantity) exceeds the maximum injection quantity that can be injected by the single normal injector 21, but the actual injection quantity does not exceed the maximum injection quantity that can be injected by the single normal injector 21. However, intake air quantity is controlled to realize a target air-fuel ratio in accordance with the injection quantity of the two injectors (i.e., the request injection quantity). Therefore, if the actual injection quantity is restricted with the maximum injection quantity that can be injected by the single normal injector, the intake air quantity becomes excessive with respect to the actual injection quantity and the air-fuel ratio shifts toward a lean side. In the worst case, there is a possibility that a catalyst causes excessive temperature increase due to the lean air-fuel ratio, thereby causing catalyst melting damage.